Free machining open hearth steel



capable of mac Patented May 9, 1939 UNITED STATES,

2,157,673 FREEMACHINING OPEN HEARTH STEEL James A. Ridgely, W. J.Holliday &

' poration No Drawing. Original Serial No. 148,324.

Cincinnati, Ohio, assignor to I 0., Indianapolis, Ind., a corapplicationJune 15, 1937, Divided and this application January 8, 1938, S

erial No. 184,025

2 Claims. (cm-123) In the higher carbon range, SAE 1040 has a Thisinvention relates to a new free machining open hearth steel havingproperties not heretofore developed in such steels. In the lower carbon.ranges, the new steel has the properties of a case hardening steelhaving high ductility and tensile strength. In the higher carbon ranges,the new steel is suitable for heat treatment. This application is adivision of my copending applicatlon Serial No. 148,324, filed June 15,1937 in which a process of manufacturing my new steel is described andclaimed per se.

In the past, most open hearth and Bessemer free machining steels havebeen produced by increasing the sulphur and manganese content above thatof the average commercial open hearth steel, the silicon and phosphoruscontent remaining about the same. For free machining case hardeningsteels the manganese content is often run as high as 1.20% and sometimeseven to 1.50% with a sulphur content often of 0.20% and sometimes 0.30%as compared to manganese contents of 0.60% and 0.80% and sulphur contentbelow 0.05% in ordinary steels. Such steels commonly carry a phosphoruscontent of about 0.04% and one commercial Bessemer steel of this typehas a phosphorus range of from 0.09% to 0.13%. Their silicon content isusually in the range of ordinary steels and is not generally specifiedin the S. A. E. specifications since heretofore it has been consideredof small importance. Such steels are free machining steels capable ofcase hardening but have, the disadvantage of being nonuniform andsometimes brittle. This lack of, uniformity and brittleness is caused bythe formation of manganese sulphide in isolated masses knowncommercially as segregations and which weaken the bars at the pointswhere they occur. Heretofore these segregations have been considered aninescapable high sulphur and manganese content which has been foundadvantageous in producing a steel 'ning at high speeds.

Heretofore the freest .machining steels have been known as SAE X1112,SAE 1112 and SALE X1314 in the low carbon range and SAE 1040 in thehigher carbon ranges. SAE X1112 and- SAE 1112 have the best machiningqualities but are rather brittle Bessemer steels having poor ductilityand 'poor case'hardening properties. SAE X1314 is fairly good from thestandpoint of free machining and case hardening but has a low yieldpoint. Its ductility, while better than X1112 and 1112, is still ratherpoor. steels, the steel produced in accordance with this invention inthe same carbon range has superior machinability, much better ductility;sup lior case hardening properties and a much higher yield point. In.case harder, deeper case in less time and with much less warpage.

evil accompanying the As compared with these hardening itproduces a goodcompensated-ductility but is relativelypoor from the standpoint of freemachining. The new steelinthisrange has substantially the same ductilitycharacteristics as SAE'1040 but has a machinability rating whichcompares favorably with that of the low carbon steels.

. Heretofore no free machining steel having a high compensated ductilityrating has been manufactured. Steel produced in accordance with thisinvention up to 0.55% carbon has a machinability rating of at least 80,compared to SAE 1112 taken as 100. In addition, its compensatedductility rating is higher than any other free machining steel. Thecompensated ductility of steels produced hereunder is above 28 andgenerally of the order of 31--33. Compensated ductility (hereinafterreferred toas D-C rating) is calculated according to the followingformula:

D-c rating=E-F0.43C

and where E is the elongation percent in 2" for ,cold drawn material andC is the hundredths of percent of carbon.

The product likewise has a compensated machinability-strength ratingconsiderably in excess of like steels. The compensatedmachineability-strength rating is calculated according to the followingformula:

TX Y EXM 1011 where T is the ultimate tensile strength in pounds persquare inch, Y the yield point inpounds per square inch, E M the.machinability based upon SAE 1112 as 100, and C is the carbon content ofthe steel MCS rating= +C expressing in hundredths of 1%.- T, Y, E and Mare based on cold drawn material.

My new steel has an MCS rating of at least 140 and normally about 150.This compares with an MCS rating of 113 for X1112, 89 for 1112 and 102for X1314. Rigidly 15% carbon steel produced hereunder had an MCSratingof approximately My new' steel has a yield point ofat least 75,000lbs. based on a 1" rod. 4

My invention contemplates a steel having sulphur and manganese contentssufficiently high to permit cutting speeds as high or higher thanpresent steels but in which the excessive formation of manganesesulphide which produces segregation is reduced: to a minimum. Accordingto my invention, the sulphur is believed to form soluble iron sulphideswhich are uniformly distributed throughout the heat and in turnthroughout the ingot, billet and bar and which add materially to thefree machining quality of thesteel. This result is accomplished byreducing the silicon and phosphorus content, which has heretofore theelongation percentage in 2",

ture ranges. Each of these four factors contributes to the reduction ofmanganese sulphide segregations.

The preferred specification of my new steel is as follows:

Per cent Sulphur 0.18 to 0.30 Manganese 1.00 to 1.40 Phosphorus 0.02maximum Silicon 0.02 maximum The steel may be made with carbon contentsfrom 0.08 to 0.75% or higher, the lower carbon steel having excellentcase hardening characteristicsand the higher carbon steel having heattreating properties. Departure from these preferred specifications,within the usual commercial tolerances, may be made without extremelydeleterious results.

It is important that the phosphorus and silicon content be kept as lowas possible. More phosphorus or silicon than that specified abovereduces the amount of sulphur and manganese which can be absorbed by thesteel without producing segregations; Less silicon and phosphoruspermits more manganese and sulphur to be used. The manganese and sulphurcontents should be in the ratio of about 5 to 1.

In the manufacture of the steel, the furnace is preferably charged withpig iron and scrap steel or with scrap steel alone, as may be desired. Abasic flux is used, lime in the proportion of about 8% of the chargebeing the preferred flux. This is foundsufiicient to reduce thephosphorus and silicon contents to the desired minimum. The carboncontent is controlled by standard open hearth practice. Sufiicientferro-manganese is added in the furnace to give about 70% of the finaldesired manganese and sulphur contents for a steel having a finalmanganese content of 1.20 to 1.30%, standard open hearth practice beingfollowed in this respect. The amount of manganese added to this pointshould not be sufficient to cause appreciable segregations of manganesesulphide. Ordinarily the amount of manganese presentin the furnace iswell below 1%--say'.84 to .91%.

The charge is preferably poured from the furnace at the usual pouringtemperature of approximately 2850 F. and is allowed to stand in theladle until it has cooled approximately F.

or more. In the case of a charge sufficient to pour 175 tons of ingotsthis cooling requires approximately 30 minutes. At the end of thedesired cooling time, a further addition of ferromanganese is madesufiicient to bring the final manganese content to the desired amount.Free sulphur is also added at the same time if the sulphur contents ofthe original charge and the added ferro-manganese does not give thedesired final sulphur contents.

The additions in the ladle still further-lower the temperature of theheat but not sufllclently to permit solidification before pouring of theingots can be completed.

The addition of the last portion of manganese and sulphur at-a reducedtemperature as inthe ladle appears to be an extremely important factorin'reducing the formation of manganese sulphide segregations.Apparently. at this reduced temperature, the reaction i rming manganesesulphide does not take plac to so great a degree as at the highertemperature, if at all. Furthermore, the time required to solidify fromthe lower temperature is so much less than from the higher temperaturethat such manganese sulphide as may possibly be formed does not havesumcient time to segregate before the charge has solidified in the ingotmold.

After the ingots have solidified, the molds are stripped and the ingotsplaced in the soaking pit and held at about 2460 F. until ready to roll.The rolling from ingot to billet is done with the least possibletemperature drop. The billets, cut to proper length, are then reheatedfor the rolling from the billet to bar.

In the rolling of bars of the low carbon steel from the billets, thestarting temperature is about 2400 F. and the finishing temperature iskept as high as possible. Preferably "at about -1860 F. to 1880 F. Belowthis finishing temperature it is found that cracks, seams andsegregations occur which destroy in a large degree the desirableproperties of the steel. For the high carbonsteel the criticalrollingtemperatures are much lower, the preferable starting temperature beingbelow 2100 F. Higher rolling temperatures for the high carbon steelproduce a porous steel having incorrect density and excessive scale.

When used for case hardening, the new steel carburizes to the same depthin less time and gives a harder case and tougher core than othercarburizing steels, and is uniform and free from brittleness. One of itsmost important charact'eristics is its freedom from excessive warpage.This characteristic is so marked that it maybe used for parts, such asrelatively long pins with ground journals on each end, which cannot bemade from other case hardening steels. This property is due in a largemeasure to the 'uniformity of the material.

The following table indicates the relative properties of the new steeland certain other steels, referring only to those steels in the colddrawn state:

A l B I C D E F G SAE X1112... 200 to 235 to 85,000 68, 000 14 SAE l1l2.150 100 80,00064,000 l5 SAE x1314 94 79, 500 62,000 19 84E 1040 115 6094,000 83,000 16 Ridgely 0.18 carbon 190 to 210 120 85, 000 80,000 26 600 Ridgely 0.39 carbon 150 100 105, 750 81, 000 16. 5 4 48-56 Ridgely0.47 carbon to 90112,200 82,94013 2. 5 5665 Column A-Machining speeds init. per min.

Column BMachinubility rating.

Column C-Tensile strength, pounds per sq. in.

Column D-Yield point, pounds per sq. in.

Column EPerceut elongation in 2".

Column F-Torslon tests, 300 turns in 12".

Column GImpact test, it.-lbs.

The figures given for Ridgely steels are conservative averages.

The new steel not only machines more readily than comparable steel, butmachines in an entirely different manner. Instead of producing chips inthe ordinary form, long spirals of material are produced which may beseveral feet in length. Machine surfaces in the new steel have asmoother appearance and texture than surfaces machined in the samemanner with other steels.

Another important result of the new steel is increased tool life. It hasbeen found in practice that tools used in machining the new steel mayWhile the invention is particularly applicable to steels having no othermetallic contents than heretofore mentioned, it may be used with steelscontaining small amounts of other metallic elements such as nickel,chromium, molybdenum, vanadium, etc. When so used, it produces a steelhaving superior machinabllity to steels of the same class. i

' Per cent Sulphur .18 to .30 Manganese 1.00 to 1.50 Phosphorus -i .02maximum Silicon .02 maximum Carbon .08 to 0.75

and the balance being substantially all iron, said steel beingsufliciently free from segregations of manganese sulphide to have arelatively high ductility, and a compensated machinabilltystrengthrating of at least 140 based on cold drawn material.

2. An alloy steel having an approximate composition as follows:

Per cent Sulphur .18 to .30 Manganese 1.00 to 1.50 Carbon .08 to 0.75

Silicon in a percentage of commercial minimum Phosphorus in a percentageof commercial minimum the balance being substantially all iron, and suchof the manganese and sulphur as may be present in the form of manganesesulphide being sumcient finely divided and in suiilciently smallquantity to produce a. steel having a relatively high ductility. and acompensated machinabilitystrength rating of at least 140 based on colddrawn material.

JAMES A. RIDGELY.

